Can Mosquito Larvae Cause Heartworm in Dogs?

The connection between dogs, mosquitoes and heartworm infection is well-established. Once confined to the southern portion of the U.S., heartworm infection in dogs has spread throughout the country. Having a good understanding of how your pup may contract this parasite goes a long way to keeping him safe from infection.

Though larvae cause heartworm and they're transmitted by mosquitoes, mosquito larvae don't cause heartworm in dogs. If your pup drank some old water with some mosquito larvae in it, you can rest easy; he won't catch the parasite from drinking infected water. Heartworm infection is a give and take process between dogs and mosquitoes.

The mosquito is the middleman when it comes to heartworm infection. When a female mosquito bites an infected dog, she picks up microfilariae, or heartworm larvae, while she's feeding. The microfilariae develop in the mosquito for 10 to 30 days and then become infective larvae. When the mosquito bites another dog, the infective larvae are transferred into the dog's bloodstream with the bite. If the mosquito doesn't bite another dog, the larvae won't develop any further.

After the infective larvae enter the dog's bloodstream, they move to the dog's heart and adjacent blood vessels, where they grow into mature adults. Male heartworms reach 4 to 6 inches long and females grow to 10 to 12 inches. They mate and reproduce microfilariae -- providing yet more opportunity for other mosquitoes to become carriers -- and clog the dog's heart and blood vessels, reducing blood supply to other organs. The kidneys, liver and lung are often affected.

Symptoms of heartworm disease depend on how long the dog's been infected. Early in the infection, there usually aren't any clinical signs. A cough is often the first sign, progressing to fatigue, listlessness, intolerance to exercise, abnormal lung sounds, difficulty breathing, abnormal heart sounds and temporary loss of consciousness. Testing for heartworm infection requires a straightforward blood test. Treatment is based on the dog's infection and history, but usually requires medicine and exercise restriction, often on an inpatient basis.

Heartworm preventives can keep your dog from being infected from a carrier mosquito. Your vet can prescribe tasty chewable tablets and topical solutions as effective barriers to infection.